U.S. Pat. No. 6,625,191 entitled VERY NARROW BAND, TWO CHAMBER, HIGH REP RATE GAS DISCHARGE LASER SYSTEM, issued to Knowles, et al., on Sep. 23, 2003 (Col. 24) and U.S. Pat. No. 6,567,450, entitled VERY NARROW BAND, TWO CHAMBER, HIGH REP RATE GAS DISCHARGE LASER SYSTEM, issued to Myers, et al., on May 20, 2003 (Col. 18, lines 10-45), disclose a spatial filter between a seed laser and amplifier laser to control bandwidth, which is also said to be able to control beam size transitioning the amplifier.
U.S. Pat. Nos. 4,792,690, 6,396,062, European Published Patent Application No. WO/2001/059414, Lawrence I. Green, “New methods for characterization of laser beams for improved performance”, presented at the Automotive Laser Applications Workshop (ALAW), Dearborn, Mich. (March, 2002) relate to measuring beam parameters, such as beam profile, pointing and divergence and the like, directly or indirectly. SinTec Optronics sells a monitor for measuring UV laser light beam divergence. Measurement of beam divergence can involve measuring the beam radius at different positions, using, e.g., a beam profiler.
As discussed in A. Zhang, et al., “Novel Detecting Methods of Shack-Hartmann Wavefront Sensor at Low Light Levels,” International Symposium on Instrumentation Science and Technology, Journal of Physics: Conference Series 48, pp. 190-195 (2006), a Shack-Hartmann wavefront sensor (“SHWFS”) may be composed of a micro-lens array, a matching lens and a CCD camera. The wavefront can be brought to separate foci producing an array of spots in the focal plane. Wavefront gradients can determine divergence, e.g., through using Zernike polynomials, such as annular Zernikes.
Adjusting an optical element, e.g., in the optical train forming a resonance cavity of an oscillator laser and/or the wavefront of the light in the cavity can, e.g., enhance the operation of a line narrowing module improving bandwidth, as discussed in, e.g., U.S. Pat. No. 6,556,612, issued on Apr. 29, 2003, to Ershov, et al., entitled LINE NARROWED LASER WITH SPATIAL FILTER and 6567450, issued on May 20, 2003, to Myers, et al., entitled VERY NARROW BAND, TWO CHAMBER, HIGH REP RATE GAS DISCHARGE LASER SYSTEM, as well as U.S. Pat. Nos. 5,095,492, 5,970,082, 6,094,448, 6,493,374, 6,496,528, 6,778,584 and 7154928, disclosing various apparatus and methods for modifying the interaction of the wavefront of the laser light and/or the dispersive face of the dispersive optic, including a deformable center wavelength selection mirror.
According to the on-line Encyclopedia of Laser Technology, edited by Dr. Rudiger Paschotta, http://www.rp-photonics.com/encyclopedia.html, different quantitative definitions of beam divergence are common. Encyclopedia of Laser Technology, Rudiger Paschotta, Ed., http://www.rp-photonics.com/encyclopedia.html. One definition is the derivative of the beam radius with respect to the axial position in the far field distance from the waist, which can also depend on the definition of beam radius. For Gaussian beams, one normally uses a beam radius definition based on the point with 1/e2 times the maximum intensity. For non-Gaussian profiles, an integral formula can be used. Beams with very small divergence, i.e., with approximately constant beam radius over significant propagation distances, are called collimated beams.
The above referenced '193 Published Patent Application discloses a set and forget lens arrangement divergence control mechanism intermediate a seed laser and amplifier laser for laser annealing applications to create a converging beam entering the amplifier laser to funnel more of the beam into the amplifier discharge region to increase output beam pulse energy and to improve the output collimation entering the annealing apparatus optical train, by matching the negative lens effect of the discharge in the amplifier discharge region.
Applicants propose improvements in the ability to periodically and/or actively control seed beam parameters, including divergence, beam shape and size and wavefront within the amplifier gain medium as the seed beam is amplified in the amplifier laser portion of a seed laser/amplifier laser arrangement, in order to improve output parameters of the amplifier laser such as pulse energy, and divergence, through an adjustable control of such beam divergence/wavefront and/or beam shaping and sizing between the seed laser and amplifier laser. In this manner, applicants propose to modify at least one output parameter of the amplifier laser to improve the ability to optically manipulate the output beam from the amplifier laser to form an elongated very narrow beam for such applications as laser annealing, e.g., for crystallizing thin films for the better formation of thin film transistors, OLEDs and the like in the crystallized thin film. This may make the cost of manufacturing a variety of types of such things as flat panel displays more uniform and economical.